In a cellular mobile communication system a mobile device wishing to access a cell must first undertake a cell search procedure. The cell search procedure typically comprises a series of synchronization stages by which the mobile device determines parameters that are necessary to demodulate the downlink and to transmit uplink symbols with correct timing. In multi radio access technology systems the cell search procedure is performed for a plurality of radio access technologies. For example, the multi radio access technology system may comprise GSM (Global System for Mobile communications), WCDMA (Wideband Code Division Multiple Access) and LTE (Long Term Evolution). The mobile device then undertakes the cell search for any radio access technology (RAT) it can operate. Specifically, when the mobile device is switched on, the mobile device has no knowledge of the exact deployment, in particular if it is switched on after traveling to a new location, e.g. after leaving an airplane in another country with different deployment. In order to gain access to a cellular multi RAT network the following steps are typically performed:
For each RAT of a plurality of R RATs                For each frequency band occupied by a RAT                    S1. For each possible frequency channel of a plurality of N frequency channels:                            a.) Tune the radio to the frequency channel.                b.) Measure the energy in the frequency channel.                                    S2. Sort the channels in descending order and pick P channels having highest energy.            S3. On these P channels having highest energy, attempt RAT specific cell search.                        
Sensing the energy is however extremely time-consuming because the radio is tuned for every frequency channel and then energy measurement is performed. Furthermore, in order to achieve statistically stable results and thus avoiding missing cells or false detections, typically stages S1 and S3 have to be repeated multiple times. Denoting the repetition factor by M, and assuming R RATs then the radio has to be tuned R*N*M times. This is a very time consuming process. Furthermore, it is a power consuming process as the radio is power on for a long time. It directly affects user experience, as a user of the system will notice the delay imposed by the cell search when the mobile device attaches to a cell. For the time the mobile device takes to accomplish the cell search procedure no network service will be available to the user.